This invention relates generally to strut type suspension members which utilize airsprings in conjunction with a damping member contained therein. In particular, conventional hydraulic shock absorbers provide the damping means and rolling lobe type airsprings provide the load support. The geometry used on helical spring strut suspensions for automobiles is such that the vehicle mass produces an angular displacement or torque which causes bending of the strut. This bending moment to the strut causes binding of the shock absorber piston which results in ride harshness. This harshness is pronounced at low amplitude undulation of the vehicle.
Methods known for creating horizontal acting side load in a vehicle suspension strut incorporating a hydraulic shock absorber and an airspring include utilizing an airspring piston eccentrically mounted on the shock absorber to create a non-symmetric rolling lobe in the flexible member of the airspring. Another alternative approach is to mount the airspring offset and at an angle to the shock absorber rod.
Yet another method includes cutting the flexible member of the airspring in a plane oblique to the shock axis and mounting the angled flexible member on an airspring to create an asymmetric roling lobe. All of these design methods create a degree of side load acting force which counteracts the bending torque placed on the strut rod by the mass of the vehicle. However, each of these methods delivers a limited amount of side load compensating force and it is highly desirable to be able to augment these side load compensating forces by utilizing additional side and compensating features in the strut design. It is to this objective of augmenting the side load compensating capability of an airspring based suspension strut that this invention is directed.
The object of this invention is to provide a suspension strut utilizing an airspring which generates side load compensating force. The force counteracts the bending torque created by the mass of the vehicle in operation and minimizes stiction in the hydraulic damper of the strut. This yields a softer ride. The airspring gives the ability to achieve variable spring rates as well as a constant vehicle height maintainable regardless of load by adjusting the internal pressure of the airspring portion of the strut. The side load compensating force is achieved by utilizing a partial restraining sleeve which restricts the radial expansion of the flexible member of the airspring around a limited portion of the circumference of the airspring. The partial restraining sleeve is positioned diametrically opposite to the line of action desired for the side load compensating force. The point of contact of the partial restraining sleeve to the flexible member is at a lesser distance from the strut axis than the unrestrained inflated radius of the flexible member of the airspring. This restraint of the flexibe member on only a portion of its circumference creates a side load compensating force on the airspring portion of the strut thereby providing the ability to offset the bending torque exerted by the sprung mass of the vehicle in which the suspension strut is mounted.
In another embodiment of the invention the partial restraining sleeve forms a part of a detachable volume can which is in pneumatic connection with the working volume of the airspring. This embodiment has the advantage of increasing the volumetric size of the airspring member while using little additional space. This is a substantial advantage in a vehicle suspension system in which the space envelope requirements are quite restricted and additional volume is difficult to achieve.
In other embodiments of the invention the partial restraining sleeve can be utilized along with an eccentrically mounted airspring piston or where the airspring is mounted offset and/or at an angel to the shock absorber axis of the strut.